Vulcanization of rubber and product obtained thereby



Patented May 23, 1933 UNITED STATES PATENT or-Pics ROBERT L. SIBLEY, OFNITRO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICE LABORATORIESCOMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO VULGANIZATION OF RUBBERAND PRODUCT OBTAINED THEREBY N 0 Drawing.

The present invention relates to the vulcanization of rubber and similarmater als such as gutta percha,balata and the like.

The invention is particularly directed to an improvement in thevulcanization of natural rubber wherein one of a preferred class ofmaterials activiated in the manner as herein crating properties of thismaterial are greatly improved by combining a mercaptobenzothiazole withan amino substituted diphenyl amine. It has now been found that the accelcratingproperties of a reaction product of an unsaturated base suchas an aromatic amine with a'mercaptobenzothiazole isgreatly improved byemploying such product as one component of a mixed accelerator in con-vjunction with a basic organic nitrogen containingvulcanizationaccelerator as an activator thereof.

Oneimethod whereby a mercaptobenzothiazole derivative employed as one ofthe components of the preferred accelerating composition: for example areaction product of mercaptobenzothiazole and p,p diamino diphenylmethane was prepared, is as follows. .A quantityof mercaptobenzothiazoleand p,p .diamino diphenyl. methane in the ratio of. substantially twomolecular proportions of the former to one ofthe latter wereheatedtogether until liquidation was effected after which agitation wascontinued until a uniform product was obtained. The product thus formedon cooling was agray crystalline Application fil ed March 6, 1930.Serial No. 433,798.

material. If convenient or desirable, the reaction product ofmercaptobenzothiazole and p,p diamino diphenyl methane may be preparedin the presence of an organic solvent, for example ethyl alcohol. n V

The material thus prepared was sufiiciently pure tobe capable of use asa vulcanization accelerator without further treatment. Thus a rubberstock was compounded in the usual manner comprising 100 parts of palecrepe rubber 5 parts of zinc oxide 1; parts of sulfur parts of stearicacid 75 parts of the accelerator described.

The above stock, after vulcanization by heating in a press in the wellknown manner for different periods of timeat the temperature of 40pounds of steam pressure per square inch, was found on testing topossess the following tensile characteristics.

The data set forth in Table I shows that the reaction product ofmercaptobenzothiadine as an activator thereof. Thus a rubber stock wascompounded comprlsing 100 parts of pale crepe rubber 5 parts of zincoxide 3 parts of sulfur 2 parts of stearic acid 0.3 parts of thereaction product of mercaptobenzothiazole and p,p diamino diphenylmethane hereinbefore described 0.3 parts of diphenyl guanidine.

Upon curing and testing the vulcanized rubber product, the tensile datatabulated in Table II were obtained.

Table II Modulus of elasticity in cute lbs/in at elongations of UltimateLbs. tion per steam lbs/m cent Time pres 300% 500% 700% sure 10 minutes-40 148 379 1430 2515 800 minutes. 40 271 833 3135 3455 745 minutes- 3181043 3790 3035 710 minutes 40 364 1070 3780 600 It is thus shown fromthe data hereinbefore set forth that the reaction product ofmercaptobenzothiazole and p,p diamino diphenyl methane itself is a verydesirable and effective accelerator, whose accelerating prop-- ertiesare greatly improved by the addition thereto of an organic nitrogencontaining basic accelerator, as an activator thereof. The acceleratingpower of the mixture of accelerators is greater than is that of eitherof its components as is evident from the results .set forth in Table IIwherein 25% less by weight of accelerator was employed in the stock thanwas used in the first example.

Another example of the preferred class of accelerators is a reactionproduct of beta use of the reaction product of beta naphthylamine andmercaptobenzothiazole alone as a vulcanlzation accelerator. A rubberstock was compounded in the usual manner comprising V 100 parts of palecrepe rubber 5 parts of zinc oxide 3 parts of sulfur 2 parts ofstcaric'acid 0.75 parts of the accelerator described.

After vulcanizing the compound rubber stock and testing the cured rubberproduct,

the tensile data set forth in Table III were obtained.

It is preferred that the reaction product of beta naphthylamme andmercaptobenzov tlnazole be employed in (3011]11110131011 with a basicorganic nitrogen containing accelerator as an activator thereof. Arubber stock was mllled 1n the usual way comprlsing 100 parts of palecrepe rubber 5 parts of zinc oxide 3 parts of sulfur 2. parts of stearicacid 3 parts of reaction product of beta naphthylamine andmercaptobenzothiazole .3 parts of diphenyl guauidine.

The compounded rubber stock was then vulcanized and the vulcanizedrubber product tested 1n the usual manner. The vulcamzed rubber wasfound-to possess the tensile data given in Table IV 1 The data set forthin Table IV shows further that the preferred class of accelerators whenactivated by a basic organic nitrogen containing accelerator comprise agroup of accelerating compounds of exceptional merit in that 20% less byweight of accelerator brought about a faster cure and produced a productof higher quality.

A reaction product of diphenyl amine and mercaptobenzothiazole wasprepared by heating together substantially equi-molecular proportions ofthese substances until the resulting product was liquid. The productthus obtained, on cooling, was a brittle solid, which upon grindingproduced a dark gray powder. This material has been employed alone as avulcanization accelerator, but preferably is employed in conjunctionwith a basic organic nitrogen containing accelerator as an activatorthereof.

On heating the compounded stock in a press in the usual manner fordifferent periods of time at40 pounds steam pressure, the reaccompoundedcomprisdiphenyl amine tion product was found to accelerate thevulcanizatlon process. It 1s preferable, however,

that this material be employed in conjunction wlth a basic organicnitrogen containing accelerator to form a mixed accelerator. Thus arubber stock was compounded comprising 100 parts of pale crepe rubber 5parts of zinc oxide 3 parts of sulfur i 2 parts of stearic acid 0.3parts of the reaction product of diphenyl amine andmercaptobenzothiazole 0. 3 parts of diphenyl guanidine.

After vulcaniZing and testing the curedrubber product, it was found topossess the tensile properties given in Table V.

Table V Modulus of elasticity in Cure lbs/i11 at elongations Tensile 2 22? at break tiong r Lbs. lbs/in steam Time prw 300% 500% 700% sure i10mini1tesi- 40 l '102 326 1035 2100 840 20 minutes 40 237 643 2415 3160740 30 minutes. 40 305 805 3200 1080 755 liquidation of the reactingsubstances was effected. On allowing to cool, a gray crystalline productwas obtained which could be ground readily. The reaction productprepared as described was milled into a rubber stock comprising 100parts of pale crepe rubber "5 parts of zinc oxide 3 parts of sulfur 2parts of stearic acid 1 .75 parts of reaction product of para plienyleuediamine and mercaptebenzothiazole.

' On vulcanizing the compounded rubber stock by heating ina press for 30minutes at 40 pounds of steam pressure per square inch, a cured rubberproduct was obtained possessing a tensile at break of 3735'pounds persquare inch and an ultimate elongation of 735%. i i t i The reactionproduct of p-phenylene diamine and mercaptobenzothiazole has beenemployed in a rubber stock in conjunction with a basic organic nitrogencontaining vulcanization accelerator, for example diphenyl guanidine,and on testing the compounded rubber stock in the well known manner, themixed accelerator was found to possess accelerating qualities comparableto those hereinbefore set forth.

Another example of the preferred class of compounds that is employedpreferably in conjunction with a basic organic nitrogen containingaccelerator as an activator thereof is a reaction product ofmercaptobenzothiazole and 2,4 diamino diphenyl amine and preferably aproduct formed by reacting substantially three molecular proportions ofmercaptobenzothiazole with substantially one molecular proportlon of 2,4diamino dlphenyl amine. As one method of employ- 1ng such reactionproduct, a rubber tread stock was compounded 1n the usual mannercomprismg 100 parts of pale crepe rubber 40 parts of carbon black 10parts of zinc oxide 2 parts of stearic acid 1. 75 parts of a blendedmineral oil and rosin 3.0 parts of sulfur parts of the acceleratordescribed above .30 parts of diphenyl guanidine.

The rubber stock thus formed was vulcanized by heating 111 a press fordifferent periods of time at different steam pressures. On'testing, thevulcanized rubber product was found to possess the modulus and tenslleproperties as set forth in Table VI.

Table VI r e -arse- 101 y in s, In C at elongations of Tensile Ultlmatsa e are; %bs. s/m cent s eam Time pres 300% 500% sure 10 805 2225 3095020 10 1000 2095 4000 060 10 1278 3275 4855 070 20 1200 3000 4445 075 20l 500 3550 4390 050 20 i055 3960 5l55 040 20 1980 4280 5020 030 l 20minutes 20 2040 44 10 5200 595 The :data as set forth in Table VI showsthat the preferred class of accelerating compounds when activated by abasic organic nitrogen containing accelerator possess exceptionallydesirable accelerating. qualities. From the above data it is apparentthat the compounded rubber stock is well cured at lower steam pressuresand not over cured on continued heating under vulcanizing conditions.

.Anhydro formaldehyde aniline and chiccarbanilide have also beenemployed among rubber tread stock was compounded comprising 100 parts ofsmoked sheet rubber 40 parts of carbon black 7 10 parts of zinc oxideparts of stearic acid 2 1. 75 parts of a blended mineral oil and rosin 3parts of sulfur .875 parts of anhydro formaldehyde aniline 375 parts ofthe reaction product of substantially three molecular proportions ofmercaptobenzotbiazole and substantially one molecular proportion of 2,4diamino diphenyl amine.

On vulcanizingand testing the vulcanized rubber product, the tensiledata given 1n the following table were obtained.

Table VII Modulus of elasticity in p q Cure lbs/in 2 at elongations of20 Ultimate tater Lbs. tlon, perteam lbs/m cent 1 Time 300% 500% 700%sure 53 45 minutes- 2 10 435 2025 730 60 minutes- 10 616 2920 650 90minutes. 10 904 4305 685 30 minutes. 20 702 3040 675 45 nlinutes 20 9854050 680 60 minutes 20 1160 4425 655 90 minutes. 20 1455 4920 670 120minutes. 20 1705 4965 G45 A stock identical with that described above,with. the exception that thiocarbanilide was employed as a basic organicnitrogen containing activator accelerator in place of an- '5" hydroformaldehyde aniline, was also compounded and the mixedvulcanizationacceler-F ator thus employed therein likewise was found topossess desirable accelerating propcities. The tensile data obtained ontesting .16 the vulcanized rubber product are given in employed as basicorganic nitrogen activator accelerators in conjunction with the reactionproduct of substantially three molecular proportions ofmercaptobenzothiazole and substantially one molecular proportion of 2,4diamino diphenyl amine as a mixed accelerator in a rubber stock. Rubberstocks were compounded comprising 100 parts of pale crepe rubber 5 partsof zinc oxide 3 parts of sulfur 4 parts of the reaction product ofsubstantially'three molecular proportions of mercaptobenzothiazole andsubstantially one molecular proportion of 2,4 diamino diphenyl amine 0.0parts of each of the basic activator accelerators given above.

The different rubber stocks thus formed were vulcanized by heating in apress in a well known manner and the vulcanized rubber products thusformed were tested, and found to possess the modulus and tensile figuresgiven in Table IX which follows. In Table IX, in order to differentiatebetween the various basic organic nitrogen containing activatoraccelerators employed in the otherwise identical stocks the followingdescription is employed: 7

AcceleratorA is di ortho tolyl guanidine. Accelerator B is triphenylguanidine.

Accelerator C is hexamethylene tetramine. Accelerator D is theformaldehyde derivative of-the reaction product of substantially 9 threemolecular proportions of acetaldehyde and substantially two molecularproportions of aniline.

8 Accelerator E is di ortho tolyl thiourea. Accelerator F is metatoluene diamine. Accelerator G is triphenyl biguanide. All the foregoingproducts designated as A to G respectively, were compounded asactivators of the accelerator of the preferred 65 phenyl biguanide amongothers have been Table VH1 type as set forth 1n the compounding recipe.Table VIII Table IX Modulus of elas- Cure Modulus of elasticity in VCure titeilty lll ltbslin f Basic lbs/in at elongations of Tensile m.'45 a 9 (mad 101150 Ultimate activaat mate Tensile at e10nga break 1 ssf tion, per Time, t g h accelerin 3 Time Steam 3007 5007 centrlilitipspres ator 300% 500% 700% lbs/1n cent pres- 0 sure sure ; s0 20A 874 1500 4750 5150 715 50 451111011005 855 2505 8 3010 090 30 B 242770 2700 3800 700 60 minutes. 10 S55 2445 3860 680 20 C 319 1145 39204415 730 00 minutes 10 1000 2500 4070 070 so 20 D 284 773 2700 4140 78530 minutes. 20 380 2505 3040 000 30 20 E 187 007 2125 8075 810 minutes.20 1055 2750 4245 080 30 20 r 183 540 1020 3705 830 00 minutes. 20 12753200 4020 005 30 20 o 204 1015 c. 4175 005 90 minutes 20 1425 3405 1605655 120 minutes 20 1505 3010 4850 055 0 w l 32 4325 700 As still furtherexamples showing the use 45 20 o 802 1440 4480 4005 705 of the preferredclass of accelerators, d1 ,1 Z38 ortho tolyl guanidine trl phenylguanldine, g 38g hexamcthylene tetramine, the formaldehyde 00 derivativeof the ieaction product of sub 20 A 530 4520 630 stantially threemolecular proportions of 60 20 B 301 1005 3610 4600 760 I 00 20 o 0001480 4040 5175 735 acetaldehyde and substantially two molecu- 00 20 D248 050 3480 4305 750 0 lar proportions of anilme, d1 ortho tolyl $38thiourea, meta toluene diamlne, and tri- 20 G 400 5115 695 ployed in thepresence of an activator of basic nature.

The present invention is not limited to the specific exampleshereinbefore set forth wherein the preferred accelerators are employed.Other ratios of the compounding ingredients than those mentioned in theeX- amples as well as other well known fillers, pigments and the likemay be employed in the production of various types of rubber compounds,and are apparent to those skilled in the art to which this inventionpertains. The present invention is limited solely by the followingclaims wherein the invention is claimed as broadly as possible in Viewof the prior art.

What is claimed is:

1. The process of vulcanizing rubber which comprises heating rubber andsulfur in the presence of an accelerator comprising a reaction productof an aromatic amine and a mercaptobenzothiazole, said accelerator beingactivated during the vulcanization process by a basic organic nitrogencontaining activating vulcanization accelerator.

2. The process of vulcanizing rubber which comprises heating rubber andsulfur in the presence of an accelerator comprising a reaction productof an aromatic primary amine and a mercaptobenzothiazole, saidaccelerator being activated during the vulcanization process bya basicorganic nitrogen containing activating vulcanization accelerator.

3. The process of vulcanizing rubber which comprises heating rubber andsulfur in the presence of an accelerator comprising a reaction productof an aromatic primary diamino compound and a mercaptobenzothiazole,said accelerator being activated during the vulcanization process by abasic organic nitrogen containing vulcanization accelerator.

4. The process of vulcanizing rubber which comprises heating rubber andsulfur in the presence of an accelerator comprising a reaction productof 2,4 diamino diphenyl amine and mercaptobenzothiazole, saidaccelerator being activated during the vulcanization process by aguanidine accelerator.

5. The process of vulcanizing rubber which comprises heating rubber andsulfur in the presence of an accelerator comprising a reaction productof substantially one molecular proportion of 2,4 diamino diphenyl amineand substantially three molecular proportions of mercaptobenzothiazole,said accelerator being activated during the vulcanization process bydiphenyl guanidine.

6. The vulcanized rubber product prepared by heating rubber and sulfurin the presence of an accelerator comprising a reaction product of anaromatic amine and a mercaptobenzothiazole, said accelerator beingactivated during the vulcanization process by a basic organic nitrogencontaining vulcanization accelerator.

7. The vulcanized rubber product prepared by heating rubber and sulfurin the presence of an accelerator comprising a reaction prodnot of anaromatic primary amine and a mercaptobenzothiazole, said acceleratorbeing activated during the vulcanization process by a basic organicnitrogen containing vulcanization accelerator.

8. The vulcanized rubber product prepared by heating rubber and sulfurin the presence of an accelerator comprising a reaction prod net of anaromatic primary diamino compound and a mercaptobenzothiazole, saidaccelerator being activated during the vulcanization process by a basicorganic nitrogen containing vulcanization accelerator.

9. The vulcanized rubber product prepared by heating rubber and sulfurin the presence of an accelerator comprising a reaction product of 2,4diamino diphenyl amine and mercaptobenzothiazole, said accelerator beingac tivated during the vulcanization process by a guanidine accelerator.

10. The vulcanized rubber product prepared by heating rubber and sulfurin the presence of an accelerator comprising a reaction product ofsubstantially one molecular proportion of 2,4 diamino diphenyl amine andsubstantially three molecular proportions of mercaptobenzothiazole, saidaccelerator be ing activated during the vulcanization process bydiphenyl guanidine.

In testimony whereof I hereunto affix my signature.

ROBERT L. SIBLEY.

